The evidence provided in this chapter on obesity prevention for the adolescent population has been comprehensively searched using the Medline database, researching available systematic reviews for obesity in children and adolescents and identifying papers from experts in the field of adolescent research. The available literature has then been synthesized and integrated into this chapter with the aim of capturing best available evidence for obesity prevention in adolescents.

To implement effective health promotion and disease prevention programmes it is necessary to establish an environment that supports positive health behavior and a healthy lifestyle. Most nutrition-related diseases have their origin during childhood and adolescence, but the relationship between their development and adolescence is poorly understood. Adolescence is a crucial period in life and implies multiple physiological and psychological changes that affect lifestyle habits.

Adolescents have particular food habits and their meal choices may differ from both adults and children.¹ They also differ in other respects, having irregular eating patterns and indulging in frequent snacking and/or skipping meals, particularly breakfast.² At this stage of the lifespan, adolescents are confronted with body weight problems and pressure concerning eating (both with respect to the type of food they are eating and the amounts of food). Despite the irregular food patterns for adolescents, it is still a crucial time as dietary patterns established during childhood and adolescence continue into adulthood and have implications for the development of chronic disease, both at present and in the future.³ Irregular food habits, such as snacking, have increased over the last 25 years across all age groups but particularly in adolescents. Snacks now account for a substantially larger percentage of total daily energy and macronutrient intake than they did in the late 1970s.³

Physical activity in adolescents is on the decrease and low levels of activity seem to persist into adulthood. Not only does lack of physical activity increase a young person’s risk for overweight and obesity but may contribute to cardiovascular disease, cancer and osteoporosis in later life. The increasing lifestyle of sedentary behaviors means the development and evaluation of physical activity interventions is, therefore, a priority for the promotion of adolescent health.

Sedentary behavior in adolescence is often mentioned as risk factor in obesity development and may have a link to its increasing prevalence and severity. The increase in playing digital games, using computers and especially watching television, have been associated with obesity. The link between obesity and television viewing has suggested that there is a delayed effect of TV viewing on body fatness.⁴ This suggestion resulted from longitudinal studies, specifically focusing on girls who exceeded two hours of television viewing per day.⁴ During adolescence, boys generally tend to spend more time playing videogames than watching television. Videogames contribute more to energy expenditure than watching television.⁵ This increase in energy is very minimal and does not diminish the risk of overweight and obesity. Computer use is also a major contributor to increasing sedentary behavior but at this stage there is no evidence to suggest a link with overweight and obesity in adolescence. There is a real lack of research in this area.⁴ Overall, with screens increasingly taking up adolescents’ leisure time it is still unclear from the research whether or not sedentary behavior replaces physical activity⁴ and what the impacts are on obesity development. There is sufficient evidence to recommend that adolescents have limits placed on their time spent watching television, that video game playing should be carefully monitored, and ensure that time spent on computers does not reduce physical activity levels.⁴

A diverse variety of settings have an impact on children’s and adolescents’ behavior. Many environments and numerous stakeholders, including parents, teachers, peers and many more, can or should be involved to stimulate activity and/or improve dietary patterns. The counteracting factors are difficult for all of those involved in the prevention of overweight and obesity in adolescents. Children and adolescents are of particular focus for obesity prevention because over-weight adolescents are at elevated risk for obesity in adulthood.⁵ The evidence suggests there is a role to play from many different parties including: schools, family, individual and policy.⁶ From the evidence, it is difficult to conclude what are the best strategies to reduce overweight and obesity in adolescents. However, it is possible to suggest from those studies that have effective outcomes which strategies might have the most success in reducing overweight and obesity. The way that information and interventions are delivered will vary and also counter cultural barriers.

There are also potential differences from effects such as gender, age and ethnicity (e.g., Doak et al)⁷ and the effect of gender has been suggested to be linked to physical activity focus.⁸ The evidence is unclear with regard to age and ethnicity as the studies that focus on these determinants are few and often low on quality.⁷ Further studies are required to cross-compare ethnicity groups and stratify age groups in order to make any conclusions. This chapter provides an overview of what the key learnings are for beginning the process of reducing obesity in adolescents.

As discussed in Chapter 10 (Obesity prevention in primary school settings: evidence from intervention studies) the associated determinants that influence overweight and obesity are complex and vary across communities and cultures. The link between community and the individual is in itself an important part of obesity prevention. Communities will often have to lead and may even implement government initiatives—therefore, it is important for teachers, schools, parents, families and adolescents to be provided with the knowledge and skills that may assist in the prevention of overweight and obesity (e.g., Sluijs et al).⁹ When identifying potential strategies for what may work at community, school or home levels, it is important to remember that strategies which may be more effective are those which build on ideas for appropriate interventions derived from children’s views and experiences.¹⁰ The building of knowledge translation (see Chapter 22, Knowledge translation and exchange for obesity prevention) is the notion that there needs to be an exchange between all stake-holders. Therefore adolescents should be consulted on matters concerning the promotion of their healthy eating and physical activity behaviors.

School-based approach

A “whole school” approach (i.e., one involving all members of the school community) can be effective in promoting healthy eating.¹¹ If schools make changes to the availability of foods within their canteens/tuck-shops, complemented by classroom activities, providing information on nutrition can be effective.¹¹ Classroom-based activities that promote healthy eating have been most successful when working in small group discussions and peer-led activities. These activities can also be complemented by learning about the environmental influences on food as this has been judged effective for reported healthy eating, particularly among young women in secondary schools. It is important that teacher preparation time must be kept to a minimum in order to ensure successful implementation within classrooms.¹⁰

Currently, there is limited evidence for the effectiveness of single component interventions, such as classroom lessons alone or providing fruit-only tuck-shops.¹⁰ However, in South Wales and South-west England one particular study provided promising results, finding that children who attend schools that run fruit tuck shops are much more likely to eat fruit if they and their friends are also banned from bringing unhealthy snacks on to the school premises.¹² This parallel between school-driven initiatives and policies seems to have more impact on students than those who do not implement joint strategies. For example, changing attitudes and perspectives about what comprises a “normal” school lunch can be accelerated through school food policies.¹³

Despite the lack of evidence for implementing single component strategies, it is still important that schools continue to work towards these initiatives. Overall, school-based interventions will lead to, on average, an increase in children’s intake of fruit and vegetables equivalent to one fifth of a portion of fruit per day, and a little less than one fifth of a portion of vegetables per day.¹⁰ Strategies such as these do raise concerns that parents are no longer providing fruit and vegetables within the home or in school lunch boxes when children are being given “free” fruit or attend a school with a fruit-only tuck-shop. This is yet to be evaluated across countries, but may be an anecdotal caution when implementing such initiatives. The offering of fruit and vegetables in schools needs to be examined in more depth and for longer follow-up periods, and its effectiveness and cost–effectiveness (e.g., Pomerleau et al)¹⁴ needs to be evaluated. However, it is important to understand that a single component strategy in weight gain prevention will never do on its own. Weight gain prevention in general will have to deal with multiple determinants of obesity, targeting multiple stakeholders. Therefore, portfolios are needed with different available strategies.

Three studies evaluated school travel interventions aimed at changing the mode of children’s travel to school. Only one—a small non-randomized trial of an active commuting pack—found a significant net increase in self-reported walking on the school journey.¹⁵

Family-based approach

Parental involvement in obesity prevention is a very important factor. Parents who are motivated to change their own behavior will have a large influence on changing the behavior of their adolescent children.¹⁰ The complex make-up of families makes it difficult to provide large-scale strategies that will be effective in reducing overweight and obesity, hence, the lack of evidence for family-based approaches.

A large-scale study found that counseling and lectures on prevention by trained instructors was effective in reducing body mass index³¹. This same study also found reduced body mass index among children with risk factors for overweight and obesity who were invited with their parents to a single individual counseling session. Also, when the primary setting is not the family setting, parental involvement is important and is among the few clear determinants for success of weight gain prevention in the young.¹⁶

Further research into this area should include family-based interventions and link to theory, research and clinical practice. Health promotion programs should include one or both parents or siblings, should use different interventions for parents, children and adolescents, and should assess outcomes using valid and reliable measures (e.g., McCallum et al, 2004).

Individual approach

Accumulating 30 minutes of moderate-intensity physical activity on most days of the week substantially reduces the risk of many chronic diseases.¹⁵ Walking is a popular, familiar, convenient, and is a free form of exercise, from which many sedentary people could gain the health benefits of moderate-intensity physical activity.¹⁵ Walking may be influenced by environmental and societal conditions as well as by interventions targeted at individuals.¹⁵ The Ogilvie et al (2007) review found that interventions tailored to people’s needs, targeted at the most sedentary, or at those most motivated to changes, and delivered either at the level of the individual or household or through groups can increase walking by up to 30–60 minutes a week on average, at least in the short term.

Children’s, young peoples and parents’ views about what helps and hinders their walking and cycling involves the strong culture of car use, the fear and dislike of local environments, children as responsible transport users, and parental responsibility for their children. “Cultures of transport” vary by age, sex and location (urban, suburban or rural).¹⁷

Studies of people’s views have several implications for intervention. The most important is the need to reduce the convenience of car travel and simultaneously increase the safety of pedestrians and cyclists in residential areas and around schools. According to the research evidence, this would encourage children, young people and parents to walk and cycle, and to use public spaces more, which would strengthen overall community environments. Furthermore, this could lead to more opportunities to nurture children’s and young people’s independence in a safer environment. In the adolescent population, there is a notion of car as “cool”.¹⁷ Future strategies will need make car use appear less attractive for effectiveness in active transport to become practice in communities.

When considering studies that assess the means for overweight and obesity reduction, primary school interventions dominate the literature.¹³ Existing reviews of overweight and obesity prevention interventions generally include primary school, and even preschool, children.^7,18–21 Even with comprehensive age inclusion, these reviews are limited by the small numbers of existing interventions. For example, applying the Cochrane criteria to a review as recently as 2005 gave only 22 studies¹⁹ and more recently the 2008 update found 18 studies.²² A more inclusive set of criteria, used by another review published in 2005 resulted in only 24 interventions.⁷ An ongoing update of this review has resulted in additional information (Solerno, personal communication) with 18 new studies fitting the original criteria for the Doak et al review. However, most of these additional interventions focus on primary school children.

While age was identified as a key concern in earlier reviews, even updated numbers are insufficient for a comprehensive study of interventions in secondary schools. Some key general conclusions found in the earlier reviews, based on a pooling of results for all children, are especially relevant to the adolescent age group. The Doak et al⁷ review identified the issue of measuring overweight and obesity as a concern in assessing interventions as effective. Namely, there are discrepancies in conclusions about intervention effectiveness depending on whether heights and weights or skin-fold measures are used to assess effective outcomes. A recently submitted commentary²³ pooled the results of two reviews^7,19 to further explore the importance of outcome assessment. One key difference in the conclusions of the two reviews relates to differences in how discrepant height/weight based results were assessed for 10 studies included by both reviews. Based on height and weight results only, three of the 10 studies were assessed as effective by Summerbell et al¹⁹ whereas six were assessed as effective by the Doak et al review⁷. These differences could be explained by the focus of the Summerbell et al¹⁹ review on mean BMI over prevalence change, ²⁴ effect on slope,²⁵ or an effective skin-fold measure.²⁶

The criteria, references and definitions to be used for overweight and obesity outcomes in adolescents is a challenging issue.⁶ While the review results illustrate the importance of this issue, it is as yet unclear which measures are most valid. It is long known that the stage of maturation matters in assessing overweight and obesity risk (Wang, 2002 ³³) Furthermore, additional evidence shows that there are clear population differences in onset of puberty.²⁷ There is evidence supporting the need for adjustment for maturation with height as a proxy,²⁸ or using population specific references.² Evidence from the literature indicates that skin-folds, but not BMI, track from adolescence into adulthood.²⁹ This evidence supports the need for further clarification of measures used to assess overweight and obesity, and that skin-fold measures may provide better information in relation to long-term risks. In particular, where interventions focus on physical activity, BMI may not be appropriate as these interventions are likely to increase muscle mass even while skin-folds are reduced.¹⁶

Sustainability should become more important in future strategies to combat the obesity epidemic. It has been recently suggested²³ that weight gain prevention programs should at least take six months. Evaluations should take place long thereafter, but such long term evidence is scarce.^16,19 It is for this reason, therefore, that the International Obesity Task Force has put a strong focus on contributing factors and points of interventions, and in the range of opportunities for weight gain prevention.³⁰

Interventions are available to reduce overweight and obesity in adolescence; and it is important to understand which of them are effective for the population group. Interventions often aim to reduce BMI or skin-fold thickness. However, there are also interventions that are effective in increasing physical activity and healthy eating and decreasing sedentary behaviors. Many of these strategies require the support and involvement of several community sectors, including schools. A majority of interventions for this population group are school-based. The following evidence recommendations are from WHO (2005) KOBE expert reported in Lobstein and Swinburn.¹³ These recommendations may assist in the future direction of intervention studies:

• All interventions should include process evaluation measures and provide resources and cost estimates. Evaluation can include impact on other parties such as parents and siblings.
  
• Interventions using control groups should be explicit about what the control group experiences. Phrases like “normal care” or “normal curriculum” or “standard school PE classes” are not helpful.
  
• There is a need for more interventions looking into the needs of specific sub-populations, including immigrant groups, low-income groups, and specific ethnic and cultural groups.
  
• There is a shortage of long-term programs monitoring interventions. Long-term outcomes could include changes in knowledge and attitudes, behaviors (diet and physical activity) and adiposity outcomes.
  
• New approaches to interventions, including prospective meta-analyses, should be considered.
  
• Community-based demonstration programs can be used to generate evidence, gain experience, develop capacity and maintain momentum.
  
• There is a need for an international agency to encourage the networking of community-based interventions, support methods of evaluation and assist in the analysis of the cost–effectiveness of initiatives.
  
• Monitoring of activities and monitoring of an increased number of outcome-measures is urgently needed and will contribute importantly to childhood and adolescence obesity prevention.

1 Moreno LA, Kesting M, de Henauw S et al: How to measure dietary intake and food habits in adolescence: the European perspective. Int J Obes 2005; 29:S66–S77.

2 Moreno LA, Rodr í guez G: Dietary risk factors for development of childhood obesity. Curr Opin Clin Nutr Metab Care 2007; 10:336–341.

3 Sebastian R, Cleveland L, Goldman J: Effect of snacking frequency on adolescents’ dietary intakes and meeting national recommendations. J Adolesc Health 2008; 42 (5):503–511.

4 Rey-Lopez JP, Vicente-Rodriguez G, Biosca M, Moreno LA: Sedentary behavior and obesity development in children and adolescents. Nutr Metab Cardiovasc Dis 2008; 18:242–251.

5 Wang X, Perry AC: Metabolic and physiologic responses to video game play in 7–10 year old boys. Arch Pediatr Adolesc Med 2006; 160 (4):411–415.

6 Flodmark CE, Lissau I, Moreno LA, Pietrobelli A, Widhalm K : New insights into the field of children and adolescents’ obesity: the European perspective. Int J Obes Relat Metab Disord 2004; 28:1189–1196.

7 Doak C, Visscher T, Renders C, Seidell JC: The prevention of overweight and obesity in children and adolescents: a review of interventions and programmes. Obes Rev 2006; 7:111–136.

8 Sallis J, Buono M, Roby J, Micale F, Nelson J: Seven-day recall and other physical activity self-reports in children and adolescents. Med Sci Sports Exerc 1993; 25 (1):99–108.

9 Sluijs E, McMinn A, Griffin S: Effectiveness of interventions to promote physical activity in children and adolescents: systematic review of controlled trials. BMJ 2007; 335 (7622):703.

10 Thomas J, Sutcliffe K, Harden A et al: Children and Healthy Eating: A Systematic Review of Barriers and Facilitators. London: EPPI-Centre, Social Science Research Unit, Institute of Education, University of London, 2003.

11 Shepherd J, Harden A, Rees R et al: Young People and Healthy Eating: A Systematic Review of Research on Barriers and Facilitators. London: EPPI-Centre, Social Science Research Unit, Institute of Education, University of London, 2001.

12 Moore L, Tapper K: The impact of school fruit tuck shops and school food policies on children’s fruit consumption: A cluster randomised trial of schools in deprived areas. J Epidemiol Community Health 2008; 62:926–931.

13 Lobstein T, Swinburn B: Health promotion to prevent obesity. In: McQueen D, Jones C eds. Global Perspectives on Health Promotion Effectiveness. New York: Springer New York, 2007:125–150.

14 Pomerleau KC, Lock K, McKee M: Getting children to eat more fruit and vegetables: a systematic review. Prev Med 2006; 42 (2):85–95.

15 Ogilvie D, Foster CE, Rothnie H et al: Interventions to promote walking: a systematic review. BMJ 2007; 334:1204.

16 Doak C, Adair LS, Bentley M, Monteiro C, Popkin B: The dual burden household and the nutrition transition paradox. Int J Obes 2005; 29:129–136.

17 Brunton G, Oliver S, Oliver K, Lorenc T: A Synthesis of Research Addressing Children’s, Young People’s and Parents’ Views of Walking and Cycling for Transport. London: EPPI-Centre, Social Science Research Unit, Institute of Education, University of London, 2006.

18 Campbell K, Waters E, O’Meara S, Summerbell C: Interventions for preventing obesity in childhood. A systematic review. Obes Rev 2001; 2:149–157.

19 Summerbell CD, Waters E, Edmunds LD, Brown KS, Campbell KJ: Interventions for Preventing Obesity in Children (Review). 3. The Cochrane Collaboration. Wiley Interscience, 2005.

20 Flynn MA, McNeil DA, Maloff B et al: Reducing obesity and related chronic disease risk in children and youth: a synthesis of evidence with “best practice” recommendations. Obes Rev 2006; 7 (Suppl. 1):7–66.

21 Bluford D, Sherry B, Scanlon KS: I nterventions to prevent or treat obesity in preschool children: A review of evaluated programs. Obesity 2007; 15 (6):1356–1372.

22 Waters E, Brown KS, Campbell KJ et al: Interventions for Preventing Obesity in Children and Adolescents (Review). The Cochrane Collaboration. John Wiley & Sons Ltd Publishers, 2009, in press.

23 Doak C, Heitmann BL, Summerbell C, Lissner L. Prevention of childhood obesity—what type of evidence should we consider relevant? Obes Rev 2009 May; 10 (3):350–6.

24 James J, Thomas P, Cavan D, Kerr D: Preventing childhood obesity by reducing consumption of carbonated drinks: cluster randomised controlled trial. BMJ 2004; 328:1237.

25 Kain J, Uauy R, Albala Vio F, Cerda R, Leyton B: School-based obesity prevention in Chilean primary school children: methodology and evaluation of a controlled study. Int J Obes 2004; 28 (4):483–493.

26 Mueller MJ, Asbeck I, Mast M, Lagnaese L, Grund A: Prevention of Obesity—more than an intention. Concept and first results of the Kiel Obesity Prevention Study (KOPS). Int J Obes 2001; 25 (Suppl. 1):S66–S74.

27 Wang Y, Adair L: How does maturity adjustment influence the estimates of overweight prevalence in adolescents from different countries using an international reference? Int J Obes Relat Metab Disord 2001; 25 (4):550–558.

28 Seidell J: Dietary fat and obesity: an epidemiologic perspective. Am J Clin Nutr 2007; 67:546S–550S.

29 Nooyens A, Koppes L, Visscher T et al: Adolescent skinfold thickness is a better predictor of high body fatness in adults than is body mass index: the Amsterdam Growth and Health Longitudinal Study. Am J Clin Nutr 2007; 85 (6):1533–1539.

30 Swinburn B, Gill T, Kumanyila S: Obesity prevention: a proposed framework for translating evidence into action. Obesity 2005; 6:23–33.

31 Alexandrov AA, Maslennikova GY, Kulikov SM, Propirnij GA, Perova NV. Primary prevention of cardiovascular disease: 3-year intervention results in boys of 12 years of age. Prev Med. 1992 Jan; 21 (1):53–62.

32 McCallum Z, Wake M, Gerner B, et al: Outcome date from the LEAP (Live, Eat and Play) trial: a randomized controlled trial of a primary care intervention for childhood over-weight/mild obesity. Int J Obes (Lond) 2007; 31:630–636.

33 Wang Y. Is obesity associated with early sexual maturation? A comparison of the association in American boys versus girls. Pediatrics. 2002 Nov; 110 (5):903–910.